An accreting low magnetic field magnetar for the ultraluminous X-ray source in M82

TL;DR

This paper proposes that the ultraluminous X-ray source in M82, identified as NuSTAR J095551+6940.8, is an accreting low magnetic field magnetar, explaining its super-Eddington luminosity and rotational behavior.

Contribution

It introduces the concept of a low magnetic field magnetar as an explanation for the observed properties of the M82 X-2 source, including its super-Eddington luminosity and spin-up.

Findings

The source's luminosity and spin-up rate are consistent with accretion onto a low magnetic field magnetar.

Theoretical period range for accreting magnetars is provided.

Three observational signatures of accreting magnetars are summarized.

Abstract

One ultraluminous X-ray source in M82 is identified as an accreting neutron star recently (named as NuSTAR J095551+6940.8). It has a super-Eddington luminosity and is spinning up. For an aged magnetar, it is more likely to be a low magnetic field magnetar. An accreting low magnetic field magnetar may explain both the super-Eddington luminosity and the rotational behavior of this source. Considering the effect of beaming, the spin-up rate is understandable using the traditional form of accretion torque. The transient nature, spectral properties of M82 X-2 are discussed. The theoretical period range of accreting magnetar is provided. Three observational appearances of accreting magnetars are summarized.